1. Field of the Invention
The present invention relates to a lead frame and a method of manufacturing the same.
2. Description of the Related Art
Conventionally, a lead frame is manufactured by forming a metal plate into a predetermined shape by performing an etching process and press working on the metal plate and then depositing a necessary plating layer on the metal plate.
In lead frame manufacture performing an etching process on a metal plate, for example, a resist mask for etching is formed by attaching dry film resist to both sides of the metal plate, exposing the dry film resist using a mask with a predetermined pattern and developing the dry film resist. Then, the metal plate is formed into a predetermined lead frame shape by etching. After that, the resist mask for etching formed on both sides of the metal plate is removed, and a desired plating process is performed on the lead-frame-shaped metal plate.
Specifications of the desired plating processes include a variety of processing forms such as a lead frame having a plating layer on its entire surfaces (top surface, back surface and side surface), a lead frame partially having a plating layer, a lead frame having a plating layer only on its top surface, and a lead frame having different plating layers on its top surface and back surface from each other.
When partially forming the plating layer on the metal plate, conventionally, a method is adopted of forming a plating layer only on a necessary portion by covering the other portion on which the plating layer is not to be formed with a rubber material while using a plating jig. However, in recent years, because the lead frame has come to be formed into a fine shape, it has become difficult to produce the plating jig. Thus, a method has come to be adopted of forming a plating mask using resist, and removing the resist mask after the plating process.
When forming the lead frame via the etching process for a metal plate, in general, a resist mask for etching is formed on the metal plate, and the resist mask for etching is removed after etching the metal plate. Other than the case of forming the same plating layer on the entire surface of the lead frame, a resist mask for plating is formed on the metal plate, and the resist mask for plating is removed after the plating process. Thus, in the general lead frame manufacture, the resist mask for etching and the resist mask for plating have been separately formed and removed from each other for different processes (etching process and plating process).
In the meantime, a variety of lead frame plating process specifications is present as discussed above, and one of the plating process specifications is a combination plating form that partially forms a plating layer on tip regions of inner leads, and entirely forms a plating layer on outer leads.
FIG. 8 is a diagram illustrating a conventional plating process for performing such a form of plating process. FIG. 9 is a diagram illustrating a plating layer formed by the conventional plating process. In the manufacturing process of the above-mentioned lead frame that has the partial plating on the tip regions of the inner leads and the entire plating on the entire surface of the outer leads, when using a method of forming and removing different resist masks for different processes independently, as illustrated in FIG. 8, a plating solution 50 flows into a gap between resist masks formed on atop surface and aback surface of a lead frame during the plating, and as illustrated in FIG. 9, the adhesion of a plating layer 120 on side surfaces of an inner lead 111 cannot be prevented.
In the meantime, conventionally, Japanese Laid-Open Patent Application Publication No. 11-345895 discloses a lead frame manufacturing method that uses a single mask for different processes.
In the lead frame manufacturing method disclosed in Japanese Laid-Open Patent Application Publication No. 11-345895, resist masks for plating made of different materials are each formed on a top surface and a back surface of a metal plate, and only the resist mask on the top surface is dissolved and removed after depositing a necessary plating layer. Then, an etching process is performed on an exposed portion of the metal plate using the already deposited plating layer as a resist mask for etching, thereby forming the metal plate into a lead frame shape.
Moreover, in the technique disclosed in Japanese Laid-Open Patent Application Publication No. 11-345895, by using the undissolved and unremoved resist mask on the back surface not only as the mask for plating but also as the mask for etching, and using the plating layers formed on both sides of the top and back surfaces as an etching mask, the number of times of forming the resist masks is reduced.
However, the technique disclosed in Japanese Laid-Open Patent Application Publication No. 11-345895 in which the resist masks for plating made of different materials are formed on both side of the metal plate; the resist mask remaining on the back surface without being dissolved and removed is also used as the etching mask; and the plating layers on both sides are used as the etching mask, has a problem of easily forming the unevenness in the surfaces of the plating layers because the plating layer is influenced by the etchant.
Moreover, because plating layers are formed only at locations to be used as terminals, and thus because the plating locations cannot be selectively set at any locations on the top and back surfaces and side surfaces of inner leads, outer leads and the like, desired plating characteristics cannot be obtained.